With the booming of the Internet and portable appliances it has appeared to be necessary to transmit video data over mobile networks for low-bit rate and real-time applications. Coding techniques have been implemented for this type of applications such as, for example, the MPEG-4 or H.26L standard, these techniques being based on a block-based discrete transformation. Correction techniques for correcting the effects of blocks more specifically dedicated to low rates for correcting the blocking artifacts due to these block-based coding techniques have been developed in parallel.
The post-processing technique of a decoded digital image implemented in the MPEG-4 standard is described in the document of the International Standardization Organization ISO/IEC JTC 1/SC 29/WG 11, entitled “Technologie de l'information—Codage des objets audiovisuels—Partie 2: Visuel”, N 3056, pp. 454–56, published Jan. 31, 2000. It has for an object to correct the effects of blocks which are possibly present in MPEG-4 coded and decoded digital images. This post-processing technique is described in FIG. 1 and comprises the following steps:                a degradation evaluation step DEGR (11) of a digital image Im, which receives on the input said digital image Im and delivers a measure of the degradation DM of the image,        a classification step CLASS (12) which receives on the input a segment S(j,k) of a row or column of pixels of two adjacent blocks (Bj,bk) of said digital image Im and assigns thereto a class Ci from a set of two possible classes, a uniform class C1 and a textured class C2,        a filter step FILT (13) which receives on the input the row or column segment of pixels S(j,k) and, as a function of the measure of degradation DM, delivers or not a filtered segment S′(j,k) with the aid of the filter F1 if the segment S(j,k) is of class C1 and with the aid of the filter F2 if the segment S(j,k) is of the class C2.        
The classification and filter steps CLASS (12) and FILT (13) are applied to segments of rows or columns of pixels of two adjacent blocks and are consequently implemented in a scanning loop (14) of the segments of rows and columns of the digital image Im. Once the scanning has been effected, a filtered digital image ImF is obtained.
A major drawback of this image processing method resides in its complexity which, although of the same order of magnitude as other competitive techniques, remains prohibitive for real-time and low-bit rate dedicated applications, for example, to mobile terminals.